Credit companies were ordered by the Financial Services Authority (as it was then) to pay compensation billions to customers sold PPI insurance they didn't actually need, and gave them instructions on how this compensation should be calculated.

Closed doors: Card companies are too secretive when challenged by customers about how they calculated their compensation.

Rather than funnelling every one of the countless claims through the Financial Ombudsman Service, companies were charged with sorting out claims themselves.

They logic was that they would adhere to the ombudsman's views PPI compensation, which is that consumers should be 'put in the position they would be in now if the original problem hadn't happened.'

But banks, building societies and card companies remain frustratingly secretive about how they arrive at payout figures for individual customers.

I wrote a series of articles last year detailing a PPI victim's struggles with Barclaycard as he sought an explanation for why an initial £22,000 compensation offer had been revised down to less than £4,000.

Barclaycard steadfastly refused to provide me or the customer any workings to show how they arrived at either figure during the months I chased the story - claiming it would 'breach commercial confidentiality'.

To its credit, Barclaycard did finally agree to honour the original £22,000 offer, but this was at the end of a saga spanning almost two years, during which time even the Financial Ombudsman Service had failed to rule in favour of the customer.

Quite how applying calculations published publicly by the City regulator breached commerical confidentiality is beyond me, but it shows the battle people have to get the money they are due.

The opaque way in which companies are allowed to discharge their PPI obligations has paved the way for stories such as the one I mentioned at the start, which claims that up to £1billion may have been underpaid because firms had failed to take into account additional charges levied on customers.

The thing is, most customers will understandably be glad to have received any compensation in the first place, so can't be expected to recognise if they've been underpaid.

Even if they do, you can't blame them for not having the appetite to spend years of their life fighting tooth and nail against a stubborn, tight-lipped financial monolith.